Capacitors are a well known passive electronic circuit element that may be used to store an electric charge. A capacitor may comprise a pair of electrical conductors that are referred to as electrodes that are separated by a dielectric material (e.g., an insulator that can be polarized). Most typically, each electrode may be implemented as a flat plate-shaped structure, although other-shaped electrodes may be used (e.g., annular cylinder electrodes).
When a potential difference (V) is applied across the electrodes of a capacitor, an electric field develops across the dielectric material, causing positive charge to develop on one electrode and negative charge to develop on the other electrode. A capacitor is characterized by its capacitance (C), which is defined as the ratio of the electric charge on each electrode to the potential difference V between them. Capacitance is typically measured in farads.
One specialized type of capacitor that is known in the art is the variable capacitor. A variable capacitor has an adjustable capacitance value that may be intentionally and repeatedly changed. Variable capacitors may be adjusted by mechanical and electronic means.